1. Field of the Invention
This invention generally relates to passenger conveyors. More particularly, this invention relates to drive modules for passenger conveyors.
2. Description of the Prior Art
Passenger conveyors are well known and in widespread use. Escalators or moving walkways typically include a plurality of steps that move along a path to carry passengers from one location to another such as between floors in a building. Typical arrangements include a step chain having a plurality of links associated with the steps. The step chain moves in a loop corresponding to the loop followed by the steps. A drive module engages the step chain to cause the desired movement of the steps.
In modular conveyors, more than one drive module can be used to carry the anticipated passenger load, for example. Instead of using larger motors to compensate for the length of the passenger conveyor or the system construction, multiple drive modules may be employed. Passenger conveyors having multiple drive modules are known.
There are difficulties in utilizing more than one drive module for a passenger conveyor. One problem is associated with the spacing between the drive modules. If the spacing is not accurately controlled, the load carried by each drive module is not equal, increasing wear in the higher-loaded module(s). Further, even when accurate spacing is achieved, changes in the system over time (i.e., wear on system components or material contraction or expansion due to environmental factors) requires periodic maintenance and adjustment. Without accurate spacing between the drive modules in conventional arrangements, the portions of the step chain between the drive modules see varying amounts of compression or tension, depending on the situation.
U.S. Pat. No. 4,397,096 presents one proposed solution to this problem. That patent describes a device for measuring compression or tension on step chain links to determine whether the spacing between drive modules is accurate. While such a device may facilitate placement of the drive modules or adjustment of the modules over time, the difficulty of accurate placement and load distribution among the drive modules still exists. Even with such a device, there are additional expenses associated with the maintenance and inspection of the escalators.
Conventional arrangements include a steel truss for supporting the elevator. The truss typically includes a track or other structure for guiding the step chain links along a chain loop. Such conventional arrangements Limit the materials that are useable for making the step chain links. Specifically, steel must be used for the step chain links to avoid different thermal expansion properties between the chain and the truss. With differing materials having differing thermal expansion properties, the tension on the drive chain may change responsive to a changing environment, which then necessitates further adjustment of the escalator drive system. Making such adjustments is impractical and, therefore, conventional arrangements have only included the same material used to make the escalator truss structure and the step chain links.
There is a need for an improved arrangement that allows using multiple drive modules for a passenger conveyor. This invention provides a system that eliminates the need to control the spacing between the modules, avoids uneven distribution of forces between drive modules and overcomes the shortcomings and drawbacks of the prior art described above.